Pressure testing is used to test equipment and components across a range of industries. One example of this is the oil industry, where there is a need to test valves under a controlled pressure before they are shipped for use. New and refurbished valves are typically tested to a test pressure of 150% of their expected operating conditions to ensure that they can safely contain their contents. Such testing can result in failure of a valve. If this happens the valve could explode, resulting in fragments emanating from the failure becoming projectiles and injuring those in the area of the test. It is therefore desirable to carry out such testing in a safe enclosure, referred to herein as a test cell.
Traditionally pressure testing has been conducted either in a large open space or in various types of enclosures, constructed of brick, concrete, or ballistic Perspex™. Research has shown that these structures do not offer adequate protection to those immediately adjacent to, or in close proximity to, the enclosure in the event of a failure of an item under test where the pressurised volume in the item under is test is large and the applied pressure at failure is high. Research has shown that fragments generated in such a failure can directly penetrate these existing enclosures, or can cause the creation of fragments from outside of the enclosure due to scabbing. Scabbing is of particular concern in concrete structures as it is caused by the reflection of the compressive blast wave from the outside face of the enclosure as a tensile wave. This results in an impulsive generation of a piece of fast moving concrete that is detached from the main wall of the enclosure due to material failure of the concrete under tension.
Tests have shown that in order to reduce this risk to an acceptable level during pressure testing of a large high pressure valve (for example a 36″ (914 mm) diameter class 2500 valve), a concrete enclosure would require walls more than 4.5 m thick.
Another disadvantage of prior art test cells is their method for dissipating quasi static pressure. When a vessel under pressure fails, the resulting pressure wave can reflect off the walls of the enclosure of the test cell, resulting in a pressure wave with a greater impulse due to the addition of incident and reflected pressure pulses. The pressure due to this increased pressure wave is referred to as the quasi static pressure. The quasi static pressure can have enough impulse to cause a failure in the enclosure. Most current enclosures dissipate this pressure either by leaving the roof of the enclosure exposed or by having a blast roof which lifts or is frangible to dissipate and/or absorb the pressure. This has the disadvantage that portions of the roof may then themselves become projectiles, causing a hazard to those persons in the vicinity.
It is an object of the present invention to overcome one or more of the disadvantages of the prior art.